|Issaic The Breaker|
The reason these ages were corrected in the reprint is, as noted above, because they were errors. As early as the very first adventure for Pathfinder, Burnt Offerings, we have an aasimar whose age works as if she were human, and that's a pretty important element of the plot of that adventure. We've also got a tiefling in Council of Thieves who is pretty important to be someone who ages as fast as his human sister for story reasons. Up until this point, we hadn't said in print what their age categories were, and the assumption that they were identical to humans (or VERY CLOSE to huamns, at least) made for MUCH stronger stories than any other option.
When Advanced Race Guide first came out, the design team missed these bits of important information; we've since been working hard to bring the design team and the world team in closer cooperation so that the books all properly support each other, and this bit of errata is an example of that.
It's not needless meddling; it's a legitimate correction to bring the rules in sync with the story. In this case, a story that's been established for about a decade and is a fundamental part of one of our most-popular Adventure Paths. So if you prefer our "original content" (such as Rise of the Runelords/Burnt Offerings), then I'd hope you would understand why we made this change in the Advanced Race Guide reprint.
Alright, by that logic I understand the changed ages for Aaismars and Tieflings. But with the exception of a kind of minor NPC in Carrion Crown, I can't think of any Dhampirs that have been printed in any Paizo adventure. So what was the reasoning behind changing how the Dhampir age?